1. Field of the Invention
The present invention relates to a content-addressable memory (CAM), more particularly to a CAM that does not require precharging and has a low power consumption.
2. Description of the Related Art
A CAM comprises a plurality of CAM cells arranged in an array. Content stored in each row of the array is compared with search data to determine if there is a match, and a plurality of matching bits corresponding respectively to the rows are generated in accordance with the results of such a comparison.
Depending on the number of states that can be stored by the CAM cells, a CAM is classified as a binary CAM or a ternary CAM.
In the case of the binary CAM, each CAM cell comprises a data memory cell and a comparison circuit. The data memory cell stores a data bit and a complementary data bit to represent one of either a “0” or “1” state.
In the case of the ternary CAM, each CAM cell comprises a data memory cell, a mask memory cell, and a comparison circuit. The data memory cell stores a data bit and a complementary data bit, and the mask memory cell stores a mask bit and a complementary mask bit. Each of the bits of the data memory cell and the mask memory cell may represent a “0,” “1,” or “don't care” state.
For both the binary CAM and the ternary CAM, precharging is required at each comparison cycle with respect to an input terminal of a search bit, an input terminal of a complementary search bit, and an output terminal of a matching bit. As a result, overall efficiency is reduced and power consumption is increased.